Polarizing beamsplitters are commonly used in optical systems to separate unpolarized light into orthogonal polarizations, so that each orthogonal polarization component propagates in a separate direction, or to combine orthogonal polarization components arriving from separate directions into one common propagation direction. The established convention refers to the orthogonal linear polarization components as s-polarization and p-polarization. The notation of s and p refers to the plane of incidence of the light on an optical surface, which is defined as the plane containing the normal of the surface onto which the light impinges, and the direction of propagation of the light. Using the plane of incidence as reference, s-polarization is defined as the polarization in which the electrical field vector of the light waves is perpendicular to the plane of incidence, and p-polarization is defined as the polarization in which the electrical field vector of the electromagnetic field is contained within the plane of incidence.
Various types of polarizing beamsplitters are known in the art. For example, polarizing beamsplitters based on the birefringence of crystalline materials, such as Glan-laser and Glan-Thompson beamsplitters, are manufactured of high-grade calcite prisms, which are joined together. These beamsplitters transmit either p-polarization (Glan-laser) or s-polarization (Glan-Thompson), and exhibit a high degree of separation of the polarization components, as well as low absorption. The angle of deviation between the propagation directions of the two polarization components is either larger than 90° (Glan-laser) or smaller than 90° (Glan-Thompson).
Polarization beamsplitters based on a wire grid comprise an array of parallel metallic wires sandwiched between two glass prisms. The wire grid has the property of transmitting one polarization component and reflecting the other, depending upon the orientation of the wires. Due to the metallic composition, beamsplitters based on wire grids exhibit absorption losses of up to 30%.
A MacNeille polarizing beamsplitter cube comprises two glass prisms cemented together along their hypotenuse surfaces, with a multilayer dielectric coating between the prisms. The deviation between the two polarization components can be 90°. The MacNeille polarizing beamsplitter cube transmits p-polarization and reflects s-polarization.